In the study of subcortical structures that are brought into play with the propagation of paroxysmal activity from a penicillin focus in the motor cortex of the monkey, a question of importance is: which of these neuronal aggregates are essential to the full development of the experimental focal seizure? In seeking an answer, neuronal blockade of structures with previously demonstrated involvement will be brought about by a stereotaxically controlled cryoprobe. The instrument at hand permits graded cooling at its tip, that is 0.1 cm in diameter and monitored by a microthermocouple. By using non destructive degrees of cooling in selected subcortical areas, the objective will be to temporarily interrupt the progression of the paroxysmal activity, thereby demonstrating the importance of these areas in fit production.